First, Python introduction
The founder of Python is Guido van Rossum (Guido van Rossum). During the Christmas of 1989, Guido van Rossum to spend time in Amsterdam, determined to develop a new script interpreter, as an inheritance of the ABC language.
The latest Tiobe leaderboard, Python occupies the four, Python advocates beautiful, clear, simple, is a good and widely used language.
Ii. Advantages and disadvantages of Python
See the pros first
- Python's positioning is "elegant", "clear", "simple", so the Python program looks always easy to understand, beginners learn python, not only easy to get started, but also in the future, you can write those very very complex programs.
- Development efficiency is very high, Python has a very powerful third-party library, basically you want to achieve any function through the computer, the Python official library has the corresponding modules to support, directly download the call, on the basis of the base library to develop, greatly reduce the development cycle, to avoid repeating the wheel.
- High-level language ———— when you write programs in the Python language, you don't have to consider the underlying details such as how to manage the memory used by your program
- Portability ———— because of its open source nature, Python has been ported on many platforms (modified to make it work on different platforms). If you are careful to avoid using system-dependent features, all your Python programs can run on almost any system platform on the market without modification
- Scalability ———— If you need a piece of your critical code to run faster or you want some algorithms to be private, you can write some of your programs in C or C + + and then use them in your Python program.
- Embeddable ———— You can embed python into your C + + program to provide scripting functionality to your program users.
Look at the disadvantages again:
- Slow, Python runs faster than the C language, and slower than Java, so this is the main reason why many so-called Daniel disdain to use Python, but in fact, this refers to the speed of slow in most cases the user is not directly aware of, Must rely on the use of testing tools to reflect, such as you use C a program to spend 0.01s, Python is 0.1s, so c directly than Python 10 times times faster, is very exaggerated, but you can not directly perceive through the naked eye, Because a normal person can perceive the smallest unit of time is 0.15-0.4s around, haha. In fact, in most cases python has been fully able to meet your requirements for the speed of the program, unless you want to write to the speed of the most demanding search engine, in this case, of course, it is recommended that you use C to achieve.
- Code can not be encrypted, because Python is an explanatory language, its source code is stored in the form of a name, but I do not think this is a disadvantage, if your project requires that the source codes must be encrypted, then you should not use Python in the beginning to implement.
- Threads do not take advantage of multi-CPU problems, which is one of the most common drawbacks of Python, the Gil, the Global Interpreter lock (interpreter lock), is a tool that the computer programming language interpreter uses to synchronize threads so that only one thread executes at any moment, The python thread is the native thread of the operating system. On Linux for Pthread, on Windows for win thread, the execution of threads is fully dispatched by the operating system. A Python interpreter process has a main thread and the execution thread for multiple user programs. Multi-threaded parallel execution is prohibited even on multicore CPU platforms due to the existence of the Gil. A compromise solution to this problem is discussed in more detail later in the Threads and Processes section.
Iii. A brief history of Python development
- In 1989, in order to pass the Christmas holiday, Guido began to write the Python language compiler. The name Python, from Guido's beloved TV show Monty Python's Flying Circus. He hoped that the new language, called Python, would fit his ideals: create a language that is all-powerful, easy to learn, easy to use, and extensible, between C and Shell.
- 1991, the first Python compiler was born. It is implemented in C language and can call the C language library file. From birth, Python already has: classes, functions, exception handling, core data types including tables and dictionaries, and module-based expansion systems.
- Granddaddy of Python Web frameworks, Zope 1 is released in 1999
- Python 1.0-january 1994 adds lambda, map, filter and reduce.
- Python 2.0-october 16, 2000, added a memory recovery mechanism that forms the basis of the Python language framework Now
- Python 2.4-november 30, 2004, the same year now the most popular web framework Django was born
- Python 2.5-september 19, 2006
- Python 2.6-october 1, 2008
- Python 2.7-july 3, 2010
- In November, it is announced that Python 2.7 would is supported until 2020, and reaffirmed that there would is no 2. 8 release as users were expected to move to Python 3.4+ as soon as possible
- Python 3.0-december 3, 2008
- Python 3.1-june 27, 2009
- Python 3.2-february 20, 2011
- Python 3.3-september 29, 2012
- Python 3.4-march 16, 2014
- Python 3.5-september 13, 2015
Iv. Python2 and Python3
The detailed difference between PY2 and 3
PRINT is A FUNCTION
The statement have been replaced with a print () function, with keyword arguments to replace most of the special syntax of T He old statement (PEP 3105). Examples:
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Old: print"The answer is", 2*2New: print("The answer is", 2*2)Old: printx, # Trailing comma suppresses newline New: print(x, end=" ") # Appends a space instead of a newlineOld: print# Prints a newlineNew: print() # You must call the function!Old: print>>sys.stderr, "fatal error"New: print("fatal error", file=sys.stderr)Old: print(x, y) # prints repr((x, y))New: print((x, y)) # Not the same as print(x, y)! |
You can also customize the separator between items, e.g.:
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print("There are <", 2**32, "> possibilities!", sep="") |
All are UNICODE now
No longer bothered by annoying character encodings
V. Installation of Python
Windows
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1、下载安装包 https://www.python.org/downloads/2、安装 默认安装路径：C:\python273、配置环境变量 【右键计算机】--》【属性】--》【高级系统设置】--》【高级】--》【环境变量】--》【在第二个内容框中找到 变量名为Path 的一行，双击】 --> 【Python安装目录追加到变值值中，用 ； 分割】 如：原来的值;C:\python27，切记前面有分号 |
Linux, Mac
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无需安装，原装Python环境 ps：如果自带2.6，请更新至2.7 |
Vi. Variables
Variables is used to store information to is referenced and manipulated in a computer program. They also provide a labeling data with a descriptive name, so we programs can be understood more clearly by the RE Ader and ourselves. It's helpful to think of variables as containers, that's hold information. Their sole purpose is to label and store data in memory. This data can and is used throughout your program.
declaring variables
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#_*_coding:utf-8_*_name ="Alex Li" |
The code above declares a variable named: Name, and the value of the variable name is: "Alex Li"
Rules for variable definitions:
- Variable names can only be any combination of letters, numbers, or underscores
- The first character of a variable name cannot be a number
- The following keywords cannot be declared as variable names
[' and ', ' as ', ' assert ', ' Break ', ' class ', ' Continue ', ' Def ', ' del ', ' elif ', ' Else ', ' except ', ' exec ', ' finally ', ' for ', ' F ' Rom ', ' Global ', ' if ', ' import ', ' in ', ' was ', ' lambda ', ' not ', ' or ', ' pass ', ' print ', ' raise ', ' return ', ' try ', ' while ', ' WI Th ', ' yield ']
Assigning values to variables
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name ="spirit" name2 = nameprint(name,name2) name = "grace"print("What is the value of name2 now?") |
First, a new knowledge of Python
